Looks like the thief tried the BIC pen trick and almost got away with your bike.
Haven't heard of it? You can view videos of numerous people trying to unlock Kryptonite u-locks using the body of a BOC stick pen sucessfully.
Kryptonite issued a recall and replaced thousands of u-lock that use the tubular key that were prone to this form of locking picking.
I missed out on the recall, BUT Kryptonite will still replace the lock for a $20 Fee. Just pay the shipping to send the lock (and key/s if you have them, along with a $20 payment or credit card information, and Kryptonite will send you a new lock or equivalent or better quality. In your case you might get a new Evolution Series 4 u-lock (that's a $80 u-lock).
If your bike is locked outside, you need to do something before that thief comes back to finish the job. Don;t take your eyes off the bike or it's going to be gone. You can try the BIC pen trick yourself, whether you get the lock to rotate to the fully locked or the open position does not make any difference. Get the position back to unlocked and you can use the key, and if you can get it to rotate to fully unlocked you can remove it.
If you can't get the BIC trick to work, then run out and buy a new lock to double lock the bike if you don't have the tools to cut the lock off to free your bike. If you buy the new lock from REI, you can always return it after you get the replacement lock from Kryptonite (you can send the pieces in for replacement, Kryptonite u-locks come with a lifetime warranty, so package the broken/picked/cut u-lock with a $20 payment, and you may get pleasantly surprised).